Apparatus for developing electrostatic images



United States Patent 3,203,395 APPARATUS IFQR DEVELOPING ELECTRO- STATIC IMAGES Richard F. Liller, Rocky River, Ulric, assignor to Addressograph-Multigraph Corporation, Cleveland, 01110, a

corporation of Delaware Filed June 14, 1963, Ser. No. 288,626 9 Claims. (Cl. 118637) This invention relates to an improvement in the application of liquids and in particular it relates to a machine which can be used for applying low viscosity developers to sensitized sheets or the like.

At the present time developers are sometimes applied to sensitized sheets by using an applicator roller or the like to convey the liquid from a supply tank to the sheet, or by submerging the sheet in the liquid.

It has been known to use two rollers to apply to a web of material, a viscous liquid in a tray over which the web of material passes, but such devices were unsuitable for liquids of low viscosity such as Xerographic or other liquid developers.

A recent development designed for low viscosity liquids utilizes a pair of rollers at least one of which dips into the developer held in a tank, which rollers are not completely submerged in the developer, and which are driven so that their upper or outer surfaces move toward each other and are spaced sufficiently closely together to form a trough between them. This arrangement also includes end plates high enough to provide ends for the trough and prevent unrestricted flow of the low viscosity liquid from the ends of the trough, thus allowing low viscosity liquids to be handled effectively by the device. Such a device, by utilizing a pair of rollers which turn towards each other forms what could be termed a standing wave of developer which can have its upper or outer surface curved to project above the tops of the rollers, and the shape or curvature of which wave can be controlled somewhat by the speed of rotation of the rollers or by their positioning. The wave thus formed presents a highly effective pool of developer which is constantly stirred and replenished and which can be contacted by a web of paper or other base sheet on which development is to be effected. The tops of the rollers are made to project substantially above the liquid level in the tank to raise the main part of the trough itself above the liquid level.

While devices in accordance with the arrangement described above have been found to be quite effective, it would be preferable to provide a stable standing wave of low viscosity liquid if possible, without the necessity for end plates closely adjacent to the roller ends, since the clearance of these plates is somewhat critical and the stability of the wave sometimes is difficult to control. In addition there is a tendency for the side plates to project the liquid across the upper surface of a sheet being treated which in certain applications is not permissible.

The present invention has for its object the provision of an improved mechanism for providing a standing wave of low viscosity liquid in a trough between two oppositely rotating rollers such that the end plates for the trough can be dispensed with, and a stable, accurately controlled standing wave of predetermined length can be achieved.

According to the presently preferred arrangement, the foregoing object is attained by providing a rod or core member for the standing wave of suitable length and disposed within the trough formed by the primary rollers. The presence of this core member quite surprisingly presents a very stable standing wave of liquid, even with low viscosities and high roller speeds, and altogether eliminates the need for end plates placed closely adjacent to the roller ends with carefully adjusted clearances.

32%,395 Patented Aug. 31, 1965 Other objects, features and advantages will appear hereinafter as the description proceeds.

In the drawing:

FIG. 1 is a top perspective of a device embodying the present invention;

FIG. 2 is a longitudinal section through the device of FIG. 1, but showing the same filled with liquid and in operating condition, with a sheet being treated indicated in broken lines, and guides and feed rollers for the sheet being also included in diagrammatic fashion;

FIG. 3 is section taken substantially on line 3-3 of FIG. 2; and

FIG. 4 is a section similar to FIG. 2 illustrating the use of the device in conjunction with a biasing electrode.

Referring to the drawing, the device of the present invention includes a tank 11 having side walls 13, 13 in which are rotatably mounted shafts 15 and 17. The shaft 15 is drivingly connected to a roller 19 within the tank 11 and to a drive element such as pulley 21 outside the tank. The shaft 17 is similarly drivingly connected to a roller 23 within the tank and to a pulley 25 outside the tank. The axes of shafts 15 and 17 are preferably so positioned as to provide either for touching of the rollers 19 and 23, or for slight spacing therebetween just short of contact. If desired, of course, one of the shafts 15 and 17 may also be mounted for slight adjusting movement towards and away from the other.

The pulleys 15 and 17 are suitably driven in opposite directions, for example by a crossed belt 27 and motor 29, the direction of rotation, of course, being so selected that the top of the rollers 19 and 23 will move towards each other as shown in FIGS. 1 and 2. If desired, however, one of the rollers 19 and 23 could be frictionally driven merely by contact with the surface of the other. The speed of motor 29 is also preferably adjustable to accommodate various requirements.

On the basis of the structure just described, if a low viscosity liquid is placed in tank 11 to a depth sufiicient to extend well above the bottoms of rollers 19 and 23, and the motor 29 is then started, it can be understood that a bead or standing wave of liquid will tend to form in the trough, designated 31, formed between the upper portions of the rollers. However, since there is provided no means to retain the wave at the ends of the rollers, as is especially apparent in FIG. 3 where the ends of the rollers are shown well spaced from the side walls 13, the liquid will rapidly escape from the trough. Accordingly any wave which is formed would never reach significant size, but would probably remain no higher than a point well below the top levels of the rollers 19 and 23.

In equipment constructed in accordance with the present invention there is, however, also provided a rod member 33 which is disposed in the trough 31 so as to form, in effect, a core for the liquid wave. This core 33 is preferably circular in cross section and rests directly upon the rollers 19 and 23 or on a thin intervening film of the liquid on their surfaces. When thus supported, the core 33 should have a sufiicient transverse dimension to prevent any tendency to be caught in the nip of rollers 19 and 23 or to spread the axes of shafts 15 and 17, and also suflicient so that its uppermost surface is at least very nearly as high as the tops of rollers 19 and 23. When the rollers 19 and 23 are in contact or very nearly so, a suitable diameter for the .core 33 is between onequarter and one-third of the diameter of the rollers 19 and 23. More than one core member 33 may be used if desired, although a single core arrangement as shown in the drawing is presently preferred.

The core 33 is preferably so equipped as to maintain a central position lengthwise of the trough 31, and to this end is provided with axial spacers 35, 35 arranged to abut suitable ears 3'7, 37, formed asupward extensions of side \9 Walls 13, 13. If desired these spacers may constitute the projected ends of a central shaft as shown in FIG. 3.

The effect of introducing core 33 can be clearly seen in FIGS. 2 and 3 wherein there is shown a standing wave W of the low viscosity liquid. This wave has asteady non-turbulent property and a well-defined and stable outline for any given set of speed and viscosity conditions. The outline of the ends of the wave W are clearly seen in FIG. 3 wherein it is apparent that the length of core 33 accurately determines the length of the wave W. As can be seen from the drawing, the ends of the wave W drop off quickly to normal tank level beyond the ends of the core.

While the core 33 has been shown and described as having a somewhat floating relationship in the trough 3.1, it will be understood that it may also be suitably su ported on the side walls 37 with its surface in close proximity to the surfaces of the rollers 19 and 23 if desired.

In order to present a sheet S to the surface of wave W for treatment, suitable feeding and guiding equipment such as feed rollers 39 and 41, and guide plates 43 and 45 are provided. It will also be appreciated that a continuous web could be similarly treated by leading the same over a pair of guide rollers settable at the proper level with respect to the apex of the Wave W.

To place the equipment in operation, the tank 11 is filled with the liquid which it is desired to apply. In the form of the invention presently under consideration it is proposed to use the equipment for developing latent electrostatic images formed on sheets of paper each provided with a surface coating of photoconductive material. The liquid developers used for this purpose include mainly a small amount of pigment dispersed in a relatively large quantity of a volatile insulating liquid, and usually have a viscosity somewhere in the range of 1.5 centipoises to centipoises. The motor 29 is then started and operated at a suitable speed to create a standing Wave W of desired height and shape. As an indication of the appropriate speed ranges, it has been found that with rollers 19 and 23 of about one inch in diameter, speeds in the range of 250 to 400 r.p.m. are found acceptable. The wave W thus formed has notably desirable properties, being relatively stable and non-turbulent, well defined in length, and quite insensitive to small variations in roller spacing, roller speed, degree of sheet contact or viscosity of the liquid.

A sheet of photosensitive paper S, which has been provided with an electrostatic charge and then differentially exposed to light to form a latent electrostatic image in a known manner, is then passed across the top of the wave W, as by feed rollers 39, 41, FIG. 2, whereby the image on the sheet is progressively developed by the pigment particles in the developer liquid. The sheet is then dried and/or fixed in a known manner.

FIG. 4 illustrates an alternate form of the device which includes, in addition to the structure previously described, a conductive electrode in the form of plate 51 mounted slightly above and parallel to the path of the sheet S as it moves over the standing wave W. The plate 51 is mounted in insulating supports 53 and 55 and is connected to a suitable source of potential 57, the other pole of which is connected electrically to the core 33 either directly or preferably via the shafts l5 and 17 and rollers 19 and 23 as shown in FIG. 4. In the latter instance, of course, the shafts, rollers and core 33 will all be made of electrically conductive material. By maintaining a biasing voltage between the plate 51 and core 33 it is possible to control the developing action, either to speed up deposition of the pigment particles for rapid development, or to resist pigment particle deposition in the non-image areas to avoid accidental deposition and thereby maintain a clear background. The arrangement illustrated in FIG. 4 is designed to act in the first-mentioned manner, assuming the image to be negrtively charged, and for this purpose will normally have a biasing voltage of perhaps 25 to 300 volts, depending on the spacing of plate 51 from the path of sheet 5. The direction of the electric field thus provided may, of course, be adjusted to suit the sign of the charge of the image on the surface of the sheet S, and the purpose for which the biasing voltage is being applied.

While the present invention has been described in connection with the development of electrostatic images on photoconductive sheets, it will be readily realized that the principles of wave control expressed herein have more general application. For example in developing procedures involving silver halide or other chemical photographic development operations, the principles of the present invention could have effective application. In fact whenever it is desired to apply low viscosity liquids to a surface in a controlled manner the arrangement described above will serve in a very important way.

While the forms of the invention shown and described herein are admirably adapted to fulfill the objects primarily stated, it is to be understood that it is not intended to confine the invention to the forms disclosed herein, for the invention is susceptible of embodiment in other forms and variations. It will be understood, therefore, that the invention is claimed in any of its forms or modifications falling within the spirit and scope of the language employed in the appended claims.

What is claimed is:

ll. in a means for treating surfaces with low viscosity liquids which includes a tank for holding the liquid, a pair of parallel adjacent rollers positioned in said tank in close proximity to each other so as to form a trough between them and at such a level as to have at least one of their lower surfaces dipping into the liquid in said tank, but with the upper surfaces of both rollers projecting substantially above the liquid level in the said tank, means supporting said rollers in said tank for rotary motion therein, means for so driving said rollers in opposite directions as to have the upper surfaces of said rollers approaching each other and moving liquid from said tank and into said trough to form a standing Wave of liquid therein; the improvement which comprises a core member arranged in and extending lengthwise of the trough and submerged in said standing wave to provide a stabilizing means therefor.

2. A device as set forth in claim 1 in which the core member is circular in cross section.

3. A device as set forth in claim 1 in which the core member is a rod loosely resting by gravity in the trough formed by the rollers.

4. A device as set forth in claim 3 in which there are provided spacers to maintain the core member in a substantially predetermined location lengthwise of the trough.

5. A device as set forth in claim 1 in which the tank has side walls substantially spaced from the roller ends whereby the length of the standing wave is determined essentially by the length of said core member.

6. In a means for developing latent electrostatic images on sheets with low viscosity developer liquids which means includes a tank for holding the liquid, a pair of parallel adjacent rollers positioned in said tank in close proximity to each other so as to form a trough between them and at such a level as to have at least one of their lower surfaces dipping into the developer liquid in said tank, but with the upper surfaces of both rollers projecting substantially above the liquid level in the said tank, means supporting said rollers in said tank for rotary motion therein, means for so driving said rollers in opposite directions as to have the upper surfaces of said rollers approaching each other and moving de- Veloper liquid from said tank and into said trough to form a standing wave of developer liquid therein, and means for moving an electrostatically imaged sheet to 5 be developed across the surface of the standing wave of developer liquid; the improvement which comprises a core member arranged in and extending lengthwise of the trough and submerged in said standing wave to provide a stabilizing means therefor.

7. A device as set forth in claim 6 which the core member is a rod loosely resting by gravity in the trough formed by the rollers and in which the tank has side walls substantially spaced from the roller ends whereby the length of the standing wave is essentially determined by the length of said core member.

8. A device as set forth in claim 6 in which the core member is conductive, and which further includes an electrode arranged above the core member and means for impressing a biasing voltage across the gap separating the electrode and the core member.

References Cited by the Examiner UNITED STATES PATENTS 1,558,035 10/25 Millring 118-422 2,529,699 11/50 Lach 118123 2,855,895 10/58 Burns 118-259 X 2,991,754 7/61 Johnson 1l8637 WILLIAM D. MARTIN, Prim ry Examiner. 

6. IN A MEANS FOR DEVELOPING LATENT ELECTROSTATIC IMAGES ON SHEETS WITH LOW VISCOSITY DEVLOPER LIQUIDS WHICH MEANS INCLUDES A TANK FOR HOLDING THE LIQUID, A PAIR OF PARALLEL ADJACENT ROLLERS POSITIONED IN SAID TANK IN CLOSE PROXIMITY TO EACH OTHER SO AS TO FORM A TROUGH BETWEN THEM AND AT SUCH A LEVEL AS TO HAVE AT LEAST ONE OF THEIR LOWER SURFACES DIPPING INTO THE DEVELOPER LIQUID IN SAID TANK, BUT WITH THE UPPER SURFACES OF BOTH ROLLERS PROJECTING SUBSTANTIALLY ABOVE THE LIQUID LEVEL IN THE SAID TANK, MEANS SUPPORTING SAID ROLLERS IN SAID TANK FOR ROTARY MOTION THERIN, MEANS FOR SO DRIVING SAID ROLLERS IN OPPOSITE DIRECTIONS AS TO HAVE THE UPPER SURFACES OF SAID ROLLERS APPROACHING EACH OTHER AND MOVING DEVELOPER LIQUID FROM SAID TANK AND INTO SAID TROUGH TO FORM A STANDING WAVE OF DEVELOPER, LIQUID THEREIN, AND MEANS FOR MOVING AN ELECTROSTATICALLY IMAGED SHEET TO BE DEVELOPED ACROSS THE SURFACE OF THE STANDING WAVE OF DEVELOPER LIQUID; THE IMPROVEMENT WHICH COMPRISES A CORE MAMBER ARRANGED IN AND EXTENDING LENGTHWISE OF THE TROUGH AND SUBMERGED IN SAID STANDING WAVE TO PROVIDE A STABILIZING MEANS THEREFOR. 